Artificial destratification for reducing reservoir water evaporation: Is it effective?

The objective of the present study was to assess the effectiveness of artificial destratification by air-bubble plumes in reducing evaporation from reservoirs. The model DYRESM was used to model the evaporation rates and thermodynamic behaviour of a temperate reservoir in Australia under a number of combinations of destratification designs and operating conditions, comprising various numbers of ports and air-flow rates per port. The operating conditions involved continuous operation and various intermittent operating strategies. Three reservoir depths were considered, characterizing “shallow,” “medium” and “deep” reservoirs, respectively. The present study results indicated that, assuming thermal stratification develops in a reservoir (the case for the “medium” and “deep” reservoirs), artificial destratification is able to reduce surface temperatures and evaporation rates. As a result of the larger volume of cold water at the lake bottom, deeper reservoirs can derive greater benefit from the use of these systems. Being raised to the water surface by the air injected through the destratification system, the cold water from the bottom will help reduce surface temperatures. Conversely, because of their typical homothermous regime, shallow lakes are unlikely to benefit from these systems, since these reservoirs lack an abundant cold water source at the bottom. Even so, however, the reductions in evaporation from deep reservoirs are only modest, with the maximum reduction being only 2.9% for a deep lake (16.5 m) using an energy-intensive destratification system. Based on the present study, it was concluded that using destratification systems for reducing reservoir evaporation was not warranted because of the modest water savings achieved.